1. Field of the Invention
Compounds of this invention are analogues of natural prostaglandins.
Natural prostaglandins are 20-carbon atom alicyclic compounds related to prostanoic acid which has the following structure: ##STR2## By convention, the carbon atoms of I are numbered sequentially from the carboxylic carbon atom. An important sterochemical feature of I is the trans-orientation of the sidechains C.sub.1 -C.sub.7 and C.sub.13 -C.sub.20. All natural prostaglandins have this orientation. In I, as elsewhere in this specification, a dashed line ( - - - ) indicates projection of a covalent bond below a reference plane, such as those formed by the cyclopentyl ring or the bonds of a carbon atom (alpha-configuration), while a wedged line ( ) represents direction above that plane (beta-configuration). Those conventions apply to all compounds subsequently discussed in this specification.
In one system of nomenclature suggested by N. A. Nelson in J. Med. Chem., 17: 911 (1972), prostaglandins are named as derivatives or modifications of the natural prostaglandins. In a second system, the I.U.P.A.C. (International Union of Pure and Applied Chemistry) system of nomenclature, prostaglandins are named as substituted heptanoic acids. A third system of nomenclature (also described by Nelson), names all prostaglandins as derivatives or modifications of prostanoic acid (structure I) or prostane (the hydrocarbon equivalent of structure I). The latter system is used by Chemical Abstracts.
Natural prostaglandins have the general structure, ##STR3## in which L and M may be ethylene or cis-vinylene radicals five-membered ring ##STR4## may be: ##STR5##
Prostaglandins are classified according to the functional groups present in the five-membered ring and the presence of double bonds in the ring or chains. Prostaglandins of the A-class (PGA or prostaglandin A) are characterized by an oxo group at C.sub.9 and a double bond at C.sub.10 -C.sub.11 (.DELTA..sup.10,11); those of the B-class (PGB) have an oxo group at C.sub.9 and a double bond at C.sub.8 -C.sub.12 (.DELTA..sup.8,12); compounds of the C-class (PGC) contain an oxo group at C.sub.9 and a double bond at C.sub.11 -C.sub.12 (.DELTA..sup.11,12); members of the D-class (PGD) have an oxo group at C.sub.11 and an alpha-oriented hydroxy group at C.sub.9 ; prostaglandins of the E-class (PGE) have an oxo group at C.sub.9 and an alpha-oriented hydroxyl group at C.sub.11 ; and members of the F.sub..alpha. -class (PGF.sub..alpha.) have an alpha-directed hydroxyl group at C.sub.9 and an alpha-oriented hydroxyl group at C.sub.11. Within each of the A, B, C, D, E, and F classes of prostaglandins are three subclassifications based upon the presence of double bonds in the side-chains at C.sub.5 -C.sub.6, C.sub.15 -C.sub.14, or C.sub.17 -C.sub.18. The presence of a trans-unsaturated bond only at C.sub.13 -C.sub.14 is indicated by the subscript numeral 1; thus, for example, PGE.sub.1 (or prostaglandin E.sub.1) denotes a prostaglandin of the E-type (oxo-group at C.sub.9 and an alpha-hydroxyl at C.sub.11) with a trans-double bond at C.sub.13 -C.sub.14. The presence of both a trans-double bond at C.sub.13 -C.sub.14 and a cis-double bond at C.sub.5 -C.sub.6 is denoted by the subscript numeral 2; for example, PGE.sub.2. Lastly, a trans-double bond at C.sub.13 -C.sub.14, a cis-double bond at C.sub.5 -C.sub.6 and a cis-double bond at C.sub.17 -C.sub.18 is indicated by the subscript numeral 3; for example, PGE.sub.3. The above notations apply to prostaglandins of the A, B, C, D, and F series as well; however, in the last, the alpha-orientation of the hydroxyl group at C.sub.9 is indicated by the subscript Greek letter .alpha. after the numerical subscript.
The three systems of nomenclature as they apply to natural PGE.sub.3.alpha. are shown below: ##STR6## Nelson system: Prostaglandin F.sub.3.alpha. or PGF.sub.3.alpha. (shortened form);
I.U.P.A.C. system: 7-[3R,5S-Dihydroxy-2S-(3S-hydroxy-1E, 5Z-octadienyl)-cyclopent-1R-yl]-5Z-heptenoic acid; and,
Chemical Abstracts system: (5Z,9.alpha.,11.alpha.,13E,15S,17Z)-9,11,15-trihydroxyprosta-5,13,17-trien -1-oic acid.
It is important to note that in all natural prostaglandins there is an alpha-oriented hydroxyl group at C.sub.15. In the Cahn-Ingold-Prelog system of defining stereochemistry, that C.sub.15 hydroxyl group is in the S-configuration. The Cahn-Ingold-Prelog system is used to define stereochemistry of any asymmetric center outside of the carbocyclic ring in all three systems of nomenclature described above. This is in contrast to some prostaglandin literature in which the .alpha.,.beta. designations are used, even at C.sub.15.
Various derivatives and analogues of the prostaglandins described above may be synthesized. Although these derivatives do not occur as such in nature, many of them possess activity related to their parent compounds. Such synthetic derivatives and analogues include the following: